Method of suppressing hot spot in arc furnace and apparatus therefor

ABSTRACT

A method of suppressing hot spots in an electric arc furnace particularly an electric arc furnace for use in steel making and an apparatus pertaining thereto, in which one or more water cooled boxes are provided in the furnace wall. The temperature of the inner wall of the box or of the cooling water is sensed. The power supply to the electrode or electrodes is adjusted in response to the sensed temperature.

Hated States Patent 1 1 1 1 3,743,752 Furuhashi July 3,- 1973 METHOD OF, SUPPRESSING HOT SPOT IN [56] References Cited ARC FURNACE AND APPARATUS UNlTED STATES PATENTS THEREFOR 3,622,678 11/1971 Allen 13/13 [75] Inventor; Haruyoghi Fug-uha hi, Naka k 3,183,294 5/1965 Kasper 13/12 X Nagoywshil Aichpken Japan 3,190,626 6/1965 Schwabe et al 13/35 X [73] Assignee: Daido Steel Co., Ltd., Minami-ku, Primary Examiner Roy N Ema" JR Nagoyashl Japan Attorney-Woodhams, Blanchard & Flynn [22] Filed: Jan. 27, 1972 211 App]. No.: 221,278 [571 ABSTRACT A method of suppressing hot spots in an electric arc furnace particularly an electric arc furnace for use [30] Forelgn Application Pmmgy Data in steel making and an apparatus pertaining thereto, Feb. 2, 1971 Japan 46/3590 in which one or more water cooled boxes are provided in the furnace wall. The temperature of the inner wall [52] U.S. Cl. 13/12, 13/35 ofthe box or Ofthe cooling water is sensed The power [51] Illt. Cl. H051) 7/12 pp y to the electrode or electrodes is adjusted in [58] Fleld of Search 13/1, 9, 12, 13,

sponse to the sensed temperature.

7 Claims, 5 Drawing Figures PMENIEUJUL 3 ms WS'BFS FIG. 5

METHOD OF SUPPRESSING HOT SPOT IN ARC FURNACE AND APPARATUS THEREFOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of suppressing hot spots in an electric arc furnace particularly electric arc furnaces for use in manufacturing steel, and an apparatus pertaining to said method.

2. Description of the Prior Art Nowadays, in manufacturing steel by means of an electric arc furnace, it is popular to supply a large quantity of electric power, such as 1.5 2 times as much as the power supplied in the past or more, with a view to shortening the melting-down time and increasing the productivity. But this method is accompanied by the frequent occurrence of the so-called hot spots as is generally known, and therefore, there has been a demand for a means of preventing the occurrence thereof.

In this connection, the quantity of the hot spots in question is proportioned to the product obtained by multiplying the electric power per electrode by the arc voltage, and accordingly, in order to reduce this quantity, it is sufficient to effect a short are by reducing the arc voltage when the electric power is of a fixed quantity. By so doing, shortening of the melting-down time is also feasible, as is generally known. Based on this knowledge and the finding that it is most effective to apply high electric power by means of a relatively long are for the time period beginning at the time when the scrap charged in the furnace starts melting and ending at the time when the scrap in the vicinity of the electrode melts down and, thereafter to apply a large quantity of electricity by means of short arcs successively after the scrap nearest to each of the electrodes has melted down. As one of the methods to determine the melting status of scrap it has recently been proposed to change the mode of application of electricity depending on the fluctuation of current and the change of speed of the electrode drive motor.

However, since these methods as cited before all deal with measuring the applicable electrical factors in the electricity supply to the electrode it is rather difficult to determine properly the melting status of the scrap. Also recommended for this purpose is the known method of measuring the temperature of the furnace wall by means of a thermocouple buried in said furnace wall to thereby determine the exact condition of melting indirectly. This means, however, is defective in that the bricks constituting the furnace wall are apt to wear to bring about irregular thickness thereof and damage of the thermocouple buried therein due to said wear, resulting in failure in determining the exact condition of melting and, in turn, unfitness for use in suppressing the occurrence of hot spots.

SUMMARY OF THE INVENTION One object of the present invention is to provide a method for securing the suppression of the occurrence of hot spots by overcoming the defects of the known method as above, and an .apparatus relevant to such a method.

Another object of the present invention is to provide a method of suppressing hot spots by determining the exact melting condition of the scrap charged in the arc furnace and appropriately altering the mode of application of electricity to the electrodes according to the thus determined melting condition of the scrap, and an apparatus relevant to such a method.

A further object of the present invention is to provide a method of suppressing hot spots by virtue of the construction of the arc furnace wherein a part of the furnace wall constitutes a water cooled box so as to cool the bricks surrounding it and the water cooled box per se constitutes a furnace wall which hardly wears, and an apparatus relevant to such a method.

A still further object of the present invention is to provide a method of suppressing hot spots through the provision of a temperature sensor equipped on the inner surface of the water cooled box wall facing the center of the furnace, said box constituting a part of the furnace wall of the arc furnace, whereby the temperature of said surface of the box wall is sensed and, in case the thus sensed temperature reaches such a level that there is a risk of the occurrence of hot spots on the furnace wall, the power supply to the electrodes is automatically adjusted by virtue of the control system; and an apparatus relevant to such a method.

An additional object of the present invention is to provide a method of suppressing hot spots by sensing constantly the temperature of the cooling water at the inlet and outlet or a set of outlets of the water cooled box or boxes constituting a part of the furnace wall of the arc furnace in order to adjust automatically the power supply to the electrodes by virtue of the control system in case the sensed value shows that the temperature has reached such a level that there is a risk of the occurrence of hot spots on the furnace wall, and an apparatus relevant to such a method.

Yet another object of the present invention is to provide a method of suppressing hot spots by fortifying the furnace wall of an arc furnace by means of a water cooled box constituting a part of said furnace wall so as to permit application of a large quantity of electricity to the electrodes without entailing hot spots and to bring about shortening of the melting-down time to contribute remarkably to increased productivity, and an apparatus relevant to such a method.

BRIEF DESCRIPTION OF THE DRAWINGS In the appended drawings, FIG. 1 is a central vertical sectional view of the furnace portion of the first embodiment of the present invention.

FIG. 2 is a horizontal sectional view of the furnace portion shown in FIG. 1 taken along the line II-II.

FIG. 3 is a schematic representation of the control system in the above embodiment.

FIG. 4 is a schematic representation of the second embodiment of the present invention.

FIG. 5 is a schematic representation of the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to F IGS. l and 2, the electrodes 3 are fitted through the furnace roof 2 placed on the furnace wall 1. The water cooled boxes 4 are inlaid in the furnace wall 1 with each box being in substantial radial alignment with the adjacent electrode. Each water cooled box is respectively connected with the water supply line 5 and the water drain line 6. Through these lines 5 and 6, the thermocouples l7 and 18 to sense the temperature are inserted into the water cooled box 4 and their tips are welded onto the inner surface of the box wall facing the center of furnace. 12 denotes the working doorway, l3 denotes the sludging doorway and 14 denotes the tapping hole.

Referring to FIG. 3, the other ends of said thermocouples l7 and 18 are connected with the temperature sensor" 7, and this temperature sensor 7 is connected with the comparator 8 through the wire 19. The comparator 8 is further connected with the program setter 9 and the recorder with" alarm device 16 through the wires 20 and 21. The program setter 9 is connected with the tap changer 10 and the electrode regulator 11 through the wires 22 and 23, and both the tap changer l and theelectrode'regulator 11 are connected with the manual controller 15. y

In an-apparatus as set forth above, the necessary numerical value-of temperature is set in advance on the comparator Band then the cooling water is circulated within the water cooled box 4 through the water supply line and the water drain line 6. As the scrap charged in the furnace melts, the temperature of the wall sur-' face of the water cooled box 4 rises, this rise in temper- ;ature is sensed by thetemperature sensor 7, and the vthus'sensed numerical value is transmitted to the comparator 8. If the numerical value thus transmitted comes to be equalto or more than the numerical value prescribed by the comparator 8 as above, then a signal is sent to the program setter 9 and the recorder with alarm device 16; At this, the program setter 9 dispatches an instruction, whereby the tap changer l0 and the electrode regulator 11 areoperated, the power supply to the electrodes is adjusted by the tap changer 10, theelectrodes aremoved to generate short are, etc. by

' means of a conventional electrode drive motor or the like (not shown herein)by virtue of the electrode regulator 1 1, and thusthe hot spots on the furnace wall 1 are'suppressed. V i

FIGS. 4 and 5' representthe second and third embodiments,'respectively, of the present invention. In these embodiments, however, the same parts asthose in thefirst embodiment are denoted by the same numeral references so as to'dispe'nse with reiteration of the same explanation thereof.

' Referring to FIG."4, thewater supply line S'andthe ,1 water drain line 6 provided for the inlet and outlet of said water cooled box are connected with the temperature sensor 7. through the wires 24. and 25. With the melting of the scrap charged in the furnace, the temperature' of the-coolingwaterwithin the water cooled box-4 rises, thedifferfence between the temperature of the cooling water atthe inlet and theoutlet of the water cooled box 4 gradually increases,and the numerical value of this temperature difference is'sensed 'b'y the temperature sensor'7 andis transmitted to the'comparator8 f ,1 f

1 In this case, there are three water cooled boxes 4, each box being-disposed in confronting relation to an electrodef-And, it is so devised that the difference in respectively sensed by, said temperature sensor 7-, and all the temperature differences thus sensed are compared with the value'of temperature difference prescribed by the comparator 1 Referring to' FIG. 5, this embodiment comprises water cooled boxes 4' equal in number to the water cooled boxes 4fof the second embodiment, each box 4 being disposed between adjacent boxes '4 and connected'with the water supply line 5' and the water drain thetemperature of the'water at each inlet and outlet is line 6. The temperature sensor 7 is connected with the water drain lines 6 and 6' provided for the outlets of the u water cooled boxes 4 and 4' through the wires 26 and 1 26', respectively, to thereby sense the temperature difference of the cooling water at therespective outlets and to carry out the same, operation as in the foregoing embodiments on the basis of the numerical value thus sensed.

Further, though this embodiment shows a mode of disposition of the water cooled boxes wherein some are.

located close to the electrode while the rest are located intermediate the electrodes, it will also do to dispose an optional number of water cooled boxes at appropriate positions either along the circumferential direction or the vertical direction of the furnace wall. Besides, it will do to substitute a current setter for said tap changer.

Although particular preferred embodiments of the invention have been disclosed hereinabove for the purpose of illustration, it will be understood that variations the furnace in response to'saidsignal tosuppress' hot spots in the furnace.- a

2, In method for operating anelectric arc furnace, the steps comprising: flowing coolingwater through at least one box in the furnace wall, said boxhaving an inner wall constitutinga'portion of the interior wall of the furnace; directly sensing the temperature of the surface of said inner wall of said box bytemperature sensitive means in contact with said surface; generating an electricalsignal indicative of said temperature; and'adjusting the "power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the furnace.

3. Ina method for operating an electric arc furnace, the steps comprisingrflowing cooling :water through at least one box in the furnace wall, said box having an inner wall constituting a portion of the interior wallof the furnace; sensing the. difference in the temperature of the coolingwateryentering and leaving thelbox';;'genf eratingan electrical signal in response to said temperature differencewhich, is indicative ofthe temperature of the surface of eaid inner wall of said boxf and adjusting the power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the fumace. r g

4. In amethqd for operating an electric arc furnace, the steps comprising: flowing coolingwater'through a plurality of boxes located in spaced-apart relation in the fumace wall,.said boxes'each havingan inner wall constituting a portion of the interior wall of the furnace; sensing thetemperatures of the cooling water leaving the respective boxes;'generating an electrical signal in response to differences in said temperatures; and adjusting the power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the furnace.

5. In an electric arc furnace having wall means defining a melting chamber, electrode means extending into the chamber and electrical power supply circuitry for supplying power to the electrode means, the improvement which comprises: at least one water-cooled hollow box mounted in said wall means of said furnace; said box having a wall portion constituting a portion of the interior wall of the furnace; thermocouple means for sensing, and providing an electrical signal indicative of, the temperature of the inner surface of said wall portion of said box; and means in said circuitry for adjusting the power supply to the electrode means in response to said signal when the temperature sensed by the thermocouple is higher than a prescribed temperature, thereby to suppress hot spots in the furnace.

6. In an electric arc furnace having wall means defining a melting chamber, electrode means extending into the chamber and electrical power supply circuitry for supplying power to the electrode means, the improvement which comprises: at least one hollow box mounted in said wall means of said furnace, said box having a wall portion constituting a portion of the interior wall of the furnace; means for flowing cooling water through said box; means for sensing the temperatures of the cooling water as it enters and as it leaves said box; and means in said circuitry for adjusting the power supply to the electrode means when the difference of the temperatures of the cooling water leaving and entering the box is greater than a prescribed temperature difference, thereby to suppress hot spots in the furnace.

7. In an electric arc furnace having wall means defining a melting chamber, electrode means extending into the chamber and electrical power supply circuitry for supplying power to the electrode means, the improvement which comprises: a plurality of spaced-apart hollow boxes mounted in said wall means of said furnace, each of said boxes having a wall portion constituting a portion of the interior wall of the furnace; means for flowing cooling water through said boxes; means for sensing the temperatures of the cooling water leaving the respective boxes, and means in said circuitry for adjusting the power supply to the electrode means when the temperature difference of the cooling water leaving the respective boxes is greater than a prescribed temperature difference, thereby to suppress hot spots in the furnace. 

1. In a method for operating an electric arc furnace having at least one water cooled box in the furnace wall, said box having an inner wall constituting a portion of the interior wall of the furnace, the steps comprising: generating an electrical signal indicative of the temperature of said inner wall of said box; and adjusting the power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the furnace.
 2. In a method for operating an electric arc furnace, the steps comprising: flowing cooling water through at least one box in the furnace wall, said box having an inner wall constituting a portion of the interior wall of the furnace; directly sensing the temperature of the surface of said inner wall of said box by temperature sensitive means in contact with said surface; generating an electrical signal indicative of said temperature; and adjusting the power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the furnace.
 3. In a method for operating an electric arc furnace, the steps comprising: flowing cooling water through at least one box in the furnace wall, said box having an inner wall constituting a portion of the interior wall of the furnace; sensing the difference in the temperature of the cooling water entering and leaving the box; generating an electrical signal in response to said temperature difference which is indicative of the temperature of the surface of said inner wall of said box; and adjusting the power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the furnace.
 4. In a method for operating an electric arc furnace, the steps comprising: flowing cooling water through a plurality of boxes located in spaced-apart relation in the furnace wall, said boxes each having an inner wall constituting a portion of the interior wall of the furnace; sensing the temperatures of the cooling water leaving the respective boxes; generating an electrical signal in response to differences in said temperatures; and adjusting the power supply to the electrode or electrodes of the furnace in response to said signal to suppress hot spots in the furnace.
 5. In an electric arc furnace having wall means defining a melting chamber, electrode means extending into the chamber and electrical power supply circuitry for supplying power to the electrode means, the improvement which comprises: at least one water-cooled hollow box mounted in said wall means of said furnace; said box having a wall portion constituting a portion of the interior wall of the furnace; thermocouple means for sensing, and providing an electrical signal indicative of, the temperature of the inner surface of said wall portion of said box; and means in said circuitry for adjusting the power supply to the electrode means in response to said signal when the temperature sensed by the thermocouple is higher than a prescribed temperature, thereby to suppress hot spots in the furnace.
 6. In an electric arc furnace having wall means defining a melting chamber, electrode means extending into the chamber and electrical power supply circuitry for supplying power to the electrode means, the improvement which comprises: at least one hollow box mounted in said wall means of said furnace, said box having a wall portion constituting a portion of the interior wall of the furnace; means for flowing cooling water through said box; means for sensing the temperatures of the cooling water as it enters and as it leaves said box; and means in said circuitry for adjusting the power supply to the electrode means when the difference of the temperatures of the cooling water leaving and entering the box is greater than a prescribed temperature diffeRence, thereby to suppress hot spots in the furnace.
 7. In an electric arc furnace having wall means defining a melting chamber, electrode means extending into the chamber and electrical power supply circuitry for supplying power to the electrode means, the improvement which comprises: a plurality of spaced-apart hollow boxes mounted in said wall means of said furnace, each of said boxes having a wall portion constituting a portion of the interior wall of the furnace; means for flowing cooling water through said boxes; means for sensing the temperatures of the cooling water leaving the respective boxes, and means in said circuitry for adjusting the power supply to the electrode means when the temperature difference of the cooling water leaving the respective boxes is greater than a prescribed temperature difference, thereby to suppress hot spots in the furnace. 